Would you have to remove the pipes/radiators/baseboard etc for the old boiler system? 

The radiators are busted.

Only 1 of my 4 rentals has central air and I get swamped with applicants everytime I have a vacancy.If the heat source is radiators I would not mind that either. 

Are radiators, room air conditioning, and septic systems common there? 

After the walk through with an inspector we discovered that both boilers and multiple radiators were blown out from freeze damage, also some structural damage.

As soon as we found out instead of feeling sorry for ourselves we immediately started problem solving and figuring out how we were going to beat this thing and how we were going to maintain financially since my doctors were telling me I wasn't going to be capable of work.From February 2015 to December 2015 I was put through the ringer with chemo, stereotactic radiation, surgery, and some more chemo.  

Current furnace was installed in 1987 (very old) and it’s forced air furnace (no radiators)Any recommendation on what I should do?

No deliveries to worry about, no leaky tanks in the basement, cheaper fuel (for now), and works with my existing radiators.

Inspectors use XRF machines which use radiation to detect lead paint through multiple layers of paint without having to damage any surfaces. 

Again, are they window A/C and radiators?